This invention relates to manufacturing processes for electro-optic modulators based on properties of polymer dispersed liquid crystal (PDLC) material for use in testing arrays of thin film transistors (TFT). More particularly, this invention relates to manufacturing processes involving solvent-based polymer dispersed liquid crystal (PDLC).
Over the past decade, Photon Dynamics, Inc., of San Jose, Calif., has been manufacturing electro-optic modulators by an assembly process especially adapted to a class of raw material called NCAP involving a multi-step lamination process. Due to various complications, the result was relatively low yield of the final modulator. Problems included lack of surface flatness and smoothness, and edge/corner defects. The existing yield problem is related to:
Starting material. The NCAP itself is made by a slot-die coating process and has a thickness variation of up to ±1 micron according to specification. The NCAP is sandwiched between 2 pieces of 7 mil (175 micron) polymer film (Mylar®). According to its specification, the Mylar has a 10% thickness variation. Although the variation in small areas is much less, there is nevertheless up to ±1 micron thickness variations for a 73 mm square.
Process. The NCAP lamination process, which uses an optical UV adhesive, created additional thickness variations. The top layer Mylar peeling process further generated thickness variation, surface roughness, edge/corner defects, and electro-optical non-uniformity.
A transfer coating process has been disclosed in U.S. Pat. No. 6,151,153 “Modulator Transfer Process and Assembly” assigned to Photon Dynamics, Inc. However, this transfer coating process has been found to have limitations because the process cannot eliminate thickness non-uniformity of NCAP material, and because, between NCAP and a glass substrate, the process requires UV-curable adhesive. It has been found that this adhesive damages NCAP film during the process. Therefore, transfer coating is not suited to all desired assembly processes.
In a related development, the inventors have developed a direct coating process related to mechanisms for applying sensor materials. Such work is described in U.S. patent application Ser. Nos. 10/685,552 and 10/685,687 filed contemporaneously.